The prevention of watermark defect after copper/low-k CMP is a critical barrier for the successful integration of sub-100 nm devices. The water-mark can act as a leakage source and cause electrical shorts. The mechanism of water-mark formation during Cu/low-k CMP is suggested and its prevention methods are proposed in this study. A suitable surfactant treatment can improve the wettability of low-k films and reduce the watermark defects very effectively. The relatively stable low-k film surface is activated during polishing and prone to adsorb surfactant molecules during cleaning, which results in the reduction of water-marks after CMP. Another solution to eliminate water-mark is the application of IPA dryer in post CMP cleaning.